High Surf Advisory 2, NWS Honolulu, HI

Area Forecast Discussion
National Weather Service Honolulu HI
938 AM HST Fri Jan 7 2022

.SYNOPSIS...
The prevailing light winds and mostly dry weather will occasionally
be interrupted by frontal passages that bring brief increases in
winds and showers over the next week. The first front is expected to
be weak and shallow, affecting only Kauai and Oahu late tonight and
Saturday. Additional fronts are anticipated next week, and may
affect all islands.

&&

.DISCUSSION...

Light winds and mostly clear skies prevail across the islands this
morning. Sea breezes will emerge shortly in response to diurnal
heating, and inland clouds and a few showers can once again be
expected. The morning soundings out of Hilo and Lihue indicate a
slight increase in mid-level stability compared to yesterday which
will help reduce the intensity of any locally heavier showers.

A strong, zonal Pacific jet will maintain a large expanse of low
pressure across the north Pacific basin into early next week.
Locally, this will put the islands in a favored region for light
winds and land/sea breeze development with periodic interruptions
when one in a series of mid-latitude systems north of 30N deposits a
weakening cold front into the forecast area.

The first such front will arrive over the western end of the state
tonight and is evident on local satellite imagery around 25N/165W at
press time. As the dynamic forcing supporting this feature lifts
northward the tail end of the front will weaken, become
increasingly shallow, and decelerate as it advances toward Kauai
after midnight and Oahu during the predawn hours. As the gradient
backs to a more northwesterly direction tonight, clouds and a few
showers will focus over northwestern and north-facing slopes of
Kauai while land breezes bring clearing to the remaining islands.
Sea breezes will again emerge on Sunday as the front dissipates
over the middle of the state. The remnant band of moisture may
provide a boost to clouds/showers over the island interiors.

Upper-level flow across the Pacific will become more amplified
next week but will remain very progressive. As a result,
confidence is higher than normal in the expectation for periodic
cold frontal passages but lower than normal with respect to
timing. The next front is modeled to arrive Monday into Monday
and will bring a greater coverage of showers compared to tonight's
frontal passage given that it will have improved upper support
and a deeper moisture supply. The guidance indicates a solid push
of dry air in the wake of Monday night's front with the GFS
suggesting dewpoints falling well into the 50s on Tuesday. Sea
breezes return mid-week and persist until the next frontal
passage.

&&

.AVIATION...

Latest surface analysis reveals a cold front approaching the
islands from the northwest, surface ridging extending over the
area from the west, and a surface trough east of the Big Island.
Winds will remain light and variable today which will promote
afternoon sea breezes and an increase in cloud coverage across
most land areas. However, clouds will decrease once again during
the evening hours as land breezes resume. Mostly VFR conditions
are expected today, though isolated MVFR cigs will be possible as
through the evening.

Overnight, a quick moving cold front will pass near the islands
and increase the chance for showers over Kauai and Oahu.
Additionally, windward areas of the Big Island could see an
increase in showers and low clouds tonight through Saturday.

There are currently no AIRMETs in effect, and none are expected
through tonight.

&&

.MARINE...

A series of cold front passing north of the islands, or
approaching the islands and weakening will keep winds on the
lighter side through the weekend. High pressure north of the
islands early next week will help to boost the winds to moderate
levels.

A series of storm to hurricane force lows in the western Pacific
are expected to send several long period northwest swells to the
region as early as tonight, and into the middle of the new week.

The current northwest swell is on the decline, with advisory level
surf today along the north and west facing shores of Niihau,
Kauai, Oahu and Molokai; north facing shores of Maui; and west
facing shores of the Big Island. A new northwest swell is
expected to start showing up later today at the buoys to the
northwest of the islands, and should start showing up at the
nearshore buoys tonight. This next swell is expected to be larger
than the current swell was yesterday, resulting in advisory level
surf initially, and then warning level surf. The decision to be
made later today will be whether or not to keep the existing high
surf advisory up for the new incoming swell. Models current
suggest that surf will likely remain at advisory levels for
Niihau, Kauai, Oahu and possible Molokai most of tonight with the
existing swell subsiding and the new swell arriving. Warning
level surf is currently expected to reach these islands by
tomorrow morning. Maui and the Big Island have a greater chance
of seeing surf fall below advisory levels for a chunk of tonight,
but expect advisory level surf to reach these islands tomorrow.
Niihau, Kauai and Oahu look to have warning level surf by tomorrow
morning, with warning levels reaching Molokai later in the day.
Will make the final determination after looking at the latest
model guidance, buoy data and surf observations.

Winter time surf will continue for the north and west shores into
next week with additional northwest swells arriving in the
islands. As this next swell event declines into Monday, another
northwest swell will arrive once again boosting surf to warning
levels. Not to be outdone, as that swell declines Wednesday,
another swell will arrive to once again bring warning level surf
to the region.

With all these swells, expect seas to exceed Small Craft Advisory
(SCA) thresholds for exposed waters at various times, while winds
are expected to remain below SCA levels. Expect a SCA to be issued
by tomorrow morning for the next swell. Due to its size, most
coastal waters will likely be in this SCA. Over the weekend and
into next week, the seas over the waters near Kauai and the
windward waters of the smaller islands will likely remain at SCA
as each of the swells arrive. Waters to the lee of the smaller
islands and waters near the Big Island are more likely to see
periods when seas will drop below SCA levels early next week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST this evening for Niihau-Kauai
Leeward-Waianae Coast-Oahu North Shore-Maui Windward West-Kona-
Kohala-Kauai North-Molokai Windward-Molokai North-Molokai West-
Maui Central Valley North-Windward Haleakala-Big Island South.

&&

DISCUSSION...JVC
AVIATION...Vaughan
MARINE...M Ballard